Class I vs. Class II changes

[swertel]

Does anyone know of a specification or standard that has a definitive explanation of the difference between a Class I and a Class II change?

--Scott

http://wertel.eng.pro

 

[btrueblood]

Um, that depends on the spec. Scott.

Sorry, circular argument, I know.

I think it was the old MIL-STD-100 (now ASTM Y14.100?) that defines drawings, said spec. refers to Configuration Management standard MIL-STD-973 which probably addresses change classifications.

 

[swertel]

MIL-STD-973 has been canceled and superseded by EIA-649 (and supplement GEIA-HB-649) which is sitting on my desk waiting for me to read. I have not read the 200+ glorious pages plus revisions of MIL-973 either.

The ASME specs (Y14.100 and Y14.35) don't give a definitive description. There is about a 1-line comment in there stating that Class I and Class II is determined based on the extent of change. Or something like that.
Or maybe it was MIL-STD-31000 that I read that line.

Either way, not definitive enough and I'm hoping that some specification or standard defines "extensive."

Thanks for the help, trueblood. I'll keep digging.

--Scott

http://wertel.eng.pro

 

[MintJulep]

They're just phrases, they have no intrinsic meaning unless you tie them to some spec or define them within a contract.

As a guess I'd say that good old "form, fit, function, or interchangeability" is the dividing line.

 

[KENAT]

Is it the difference between a 'revision' or a 'new part number'?

As others say really you need to look at the relevant spec, as long and dull as that may be.

The issue of 'new part number or revision' is covered by ASME Y14.100

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[swertel]

I consider Revision vs. New Part Number an issue for configuration management, but that may be a way to define Class I vs. Class II. Class I has no fit/form/function change so I can roll the revision while a Class II change does affect fit/form/function and I need to create a new configuration.

Yet...
I am specifically looking at revision and change control. A typical revision has to be classified as Class I or Class II. In experience, a Class I is a typo or "insignificant" drafting change. A Class II change is something that requires requalification or revalidation of the system in which the change occurs. It therefore affects what parties get to have a say regarding the change because of the cost and schedule impact to incorporate the change.

Some say only typos are Class I.
Some say typos can be corrected as an administration "revision" and the drawing not rolled to the next rev.
Some say tolerance changes are Class I, others say Class II.
Some say dimensional changes are Class I, others Class II.
Then there are alternate materials, finishes, processing requirements, etc. etc.

And then there is the definition of why classification of change matters. Is a business process supposed to be different for a Class I change compared to a Class II change? Or is it just a check box on the ECO form reminiscent of procedures developed before computerized drafting and design?

--Scott

http://wertel.eng.pro

 

[PeterStock]

For our major clients, the terms are if the old and new parts can be interchanged, it is a Class II change. If not it is a Class I change. The approval procedures are different, the Class I does cost more for validation.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[swertel]

Thanks, Peter. I may have gotten Class I and Class II reversed in my example above.

--Scott

http://wertel.eng.pro

 

[Radagast]

Where I have been employed the last few years (Aerospace) each companies definition as been 'approximately' as follows.

"Class I changes affect an item's fit, form or function. These are changes that affect an item's specifications, weight, interchangeability, interfacing, reliability, safety, schedule, cost, etc. Class II changes are changes to correct documentation or changes to hardware not otherwise defined as a Class I change."

Interchangeability has its own set of requirements as well. Where I currently work our documentation is a plagiarized version of MIL-I-8500D "Interchangeability and Replaceability of Component Parts for Aerospace Vehicles"

Mike